Composition and blank for recording sound



duce various pitch and tone impulses.

Patented Jan. 19, 1943 COMPOSITION AND BLANK FOR RECORD- ING SOUND Corliss F. Cummins and Joseph L. Shel-k, Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Michigan No Drawing. Application August 22, 1940, Serial No. 353,675

2 Claims. (Cl. l106-37) Thisinvention relates to a composition and a blank for use in recording sound. It relates particuiarly to a composition capable of use in the form of fiat sheets, strip films, or of surface coatings or sheaths on cylinders, as the receptive,

base for recording sound by the lateral embossing method.

Two principal methods are in use for recording sound. One, which may be called the cutting or engraving method, relies upon a'recording mechanism which cuts a groove of varying depth in the base employed, actually severing a strip or thread of the base material from the surface during the recording operation. The other, which may be called the embossing method, involves mere displacement of the plastic base material, usually upward and outward from the embossed groove. In vertical embossing, the groove is of varying depth, just as in the records made by the engraving method, while in lateral embossing the groove is of substantially uniform depth throughout its length, the embossing instrument and the reproducing needle used to play back the record being caused to shuttle laterally to varying distances from the mean linear path of the groove to record or to repro- It is the provision of a composition for recording sound by the lateral embossing-method to which this invention particularly relates.

For use in the lateral embossing method, it is necessary to provide a recording composition which is soft enough to permit suitable displacement by a blunt stylus, as is used in this method, and which at the same time is hard enough to permit replaying the record a suitable number of times. The composition should preferably be flexible and yet not so elastic that it shows any appreciable tendency to recover its original shape after embossing. The composition should be neither as hard as nitrocellulose, nor as brittle as wax, nor as soft as the customary cellulose derivative plastics containing the usual softenin'g quantities of solvent plasticizers.

It is accordingly an object of the invention to provide a composition, soft enough to permit suitable displacement under the action of an embossing stylus as is used particularly in the lateral embossing of sound impulses, without being so plastic or elastic as to exhibit any appreciable tendency to recover its original shape after embossing, even on long standing. It is another obiect to provide a composition as aforesaid which can be made available in the various forms used in recording sound. including flat discs, strip films, tightly adhering or easily removable coatings or sheaths for cylinders, and the like.

The invention is concerned solely with a composition and a recording blank for use as above suggested. Hence, it is believed that no further discussion of recording practice need be engaged in here, it being understood that the compositions now to be described fully meet the requirements and fulfill the objects hereinbefore set forth.

The particular composition constituting the present invention, whereby the stated objects may be attained, is one consisting essentially of Per cent by weight Ethyl cellulose -98 Non-solvent plasticizers 25- 2 As inert and harmless eifect materials there may be incorporated in the above-stated composition minor amounts of dyes, pigments, or fillers, if desired.

The ethyl cellulose used in the composition may be of any degree of etherification (i. e. of any ethoxy content) which is capable of dissolving in lacquer solvents to form a homogeneous solution. Generally speaking this includes ethyl cellulose of from about 42 to about 54 per cent ethoxy. The preferred ethyl cellulose is one of' from about 43 to about 47 per cent ethoxy content, as this is the lowest ethoxy type commercially available in uniformly soluble form for film-casting purposes, and further, this type. is fundamentally harder than the higher or standard ethoxy type of ethyl cellulose. Records made from 43-47 per cent ethoxy type of ethyl cellulose are much longer lived than those made from the standard (47.5-49 per cent) product.

The non-solvent plasticizers are materials, to be enumerated hereinafter, which are essentially incompatible with the ethyl cellulose employed. Such materials can be incorporated in ethyl cellulose by depositing the composition from a volatile mutual solvent for the two materials. If intimately mixed in colmnon solution, the deposited film will have the two components intimately intermingled without danger of the plasticizer acting as a solvent or softening agent 7 for the ethyl cellulose, it serving instead primarily as a lubricant which takes up the thrust of an embossing stylus or a reproducing needle without the ethyl cellulose-base being out while recording or reproducing sound. Examples of non-solvent plasticizers of utility in the present compositions are petrolatum (either paraflin oil or petroleum jelly), blown castor oil, and such hydrogenated vegetable glycerides as those synthetic shortenings sold as Scoco, Snowdriit," Crisco, Primex B and C," and the like, most of which are hydrogenated cottonseed oil products. Other non-solvent plasticizers include soft alkvds, such as glyceryl sebacate; oil extended alkyds, and the like. To illustrate the definition further, it may be pointed out that dibutyl phthalate and tricresyl phosphate dissolve ethyl cellulose on warming, while none of the products above-listed exhibit any solvent eiIect under these conditions.

To illustrate the manner in which the compositions of the invention may be used in preparing sound record blanks, the following examples are given.

Example 1 A mixture of 85 parts of ethyl cellulose (46 per cent ethoxy) and 15 parts by weight of blown castor oil (Baker's No. 16) was dissolved to form a solution of 15 per cent by weight concentration in a mixture of 80 parts of toluene and 20 parts of ethanol by volume. The so-formed dope was used to cast films from which blank discs were cut for recording purposes. The dope was also used to coat, by dipping, a metal cylinder 5.1 inches in diameter with a superficial sheath 0.005 inch thick. The sheath was slipped from the cylinder, when dry, and was cut into loops 3.5 inches wide. The loops were used for voice recording by the lateral embossing method, as were the discs previously mentioned. The blanks easily took the embossed impressions and retained them indefinitely without any detectable decrease in the fidelity of reproduction on aging and replaying.

Example 2 A number of disc-form recording blanks about 0.015 inch. thick and of sizes varying up to about 16.5 inches in diameter were prepared from high concentration i20-35 per cent) solutions of the composition employed in Example 1, as well as from various mixtures of 90 parts ethyl cellulose (about 43-47 per cent ethoxy) and parts of one or a mixture of the non-solvent plasticizers:

Water-white paramn oil (liquid petrolatum) "Primex B and C" Petroleum jelly (white Vaseline") Crisco" The blanks produced were smooth and flexible. and were not greasy or oily to the touch. They retained flexibility indefinitely. When used to record sound in a Memovox recorder, by the embossing method, the recordings were found to be highly intelli ible and free from surface noises. The flexible records are easily stored in a filing cabinet, about discs requiring only 1 inch of file space. a

The invention has been illustrated with respect to the use of non-solvent plasticizers as the sole modifying agent for the ethyl cellulose. It is possible, as well, to employ some of the customary solvent-type or softening plasticizers as adjuncts to the non-solvents employed, provided always that the total amount of plasticizers of all kinds in the compositions is not over 25 per cent of the whole, and further, that in general the non-solvent plasticizer is the predominant addition agent present.

Having now described the new composition and fitting examples both of its ingredients and of the mode whereby it may be employed in making sound recording blanks, we particularly point out and distinctly claim as our invention:

1. A record blank, particularly adapted for recording sound by the lateral embossing method, consisting essentially of from to 98 percent by weight of organo-soluble ethyl cellulose of from about 43 to about 47 per cent ethoxy content and correspondingly from 25 to 2 per cent of a hydrogenated vegetable glyceride.

2. A record blank, particularly adaptedfor recording sound by the lateral embossing method, consisting essentially of from '15 to 98 per cent by weight of organo-soluble ethyl cellulose of from about 43 to about 47 per cent ethoxy content and correspondingly from 25 to 2 per cent of 8 ydrogenated cottonseed oil.

CORLISS F. CUMMINS. JOSEPH L. SHERK. 

